the shape and size basically

USD is larger and bulgier around the wheel arch, just like the USD skirts. Also runs higher up the rear bumper. Urethane

JDM is smaller and has little to no bulge, just like the JDM skirts. Also made of FRP

best comparo pics of the two kits

JDM


USDM


i ended up ordering the JDM rears from Japanparts.com. They would be a good source for JDM parts for you guys in US. They appear to be able to order any brand and part